The present invention relates in general to the joining of members using heat in a soldering, brazing or welding operation, and in particular to a new and useful process which utilizes a medium that undergoes evaporation by microexplosions at or below the joining temperature for cleaning, protecting and reducing surface tension at the surfaces of members to be joined to each other
Heat can be used to join members to each other whether they are of metallic or non-metallic materials The process of soldering includes a third material which has a lower melting temperature than that of either of the members to be connected to each other. The solder creates an intermetallic alloy with the base materials to mechanically connect them to each other Without the formation of these alloys, the solder simply lies on the surface between the members Soldering is generally divided into soft soldering which takes place at up to 300.degree. C. and usually involves solders made of tin and lead. Hard soldering which is also known as brazing uses temperatures above 400.degree. C. Solders for brazing are usually alloys of copper, silver or gold.
Welding is a joining operation which does not use a third solder material but which relies on the fusing of the members at their surfaces for connecting the members together.
Flux is commonly used for all types of thermal joining. Fluxes commonly have a solid base such as resin which is in a liquid solvent so that the flux can be sprayed or brushed onto the surfaces to be joined. The solvent evaporates at the beginning of the soldering cycle leaving only the solid flux at the joint surfaces. The flux usually fuses before reaching the joining or soldering temperatures and is at this point active for cleaning and protecting the surfaces to be joined.
The flux thus satisfies two important requirements for an effective joining. The first of these is that the surfaces to be joined are free of any contaminants such as grease, dirt or oxide. The second is that once cleaned, the surfaces must remain clean throughout the joining operation.
Even if the surfaces are cleaned by mechanical means such as scraping or machining, the heating of the joint produces new oxides and other contaminants which must be controlled. The cleaning and maintenance of clean conditions at the surfaces are required to reduce surface tension. High surface tension prevents the smooth wetting and flowing of the fused materials at the joint, whether they are the surface portion of the members to be joined together or a solder. Without an effective wetting, a solder or weld joint will not be created.
Flux is thus needed for most thermal joining operations.
During the fusing process, the flux tends to stay at the surfaces of the solder and the members to be joined. Some of the flux may invade the body of the solder, however. Some enclosure are even present after the end of the solder process. Any flux which remains around the joint must be removed either by mechanical or chemical means to avoid any subsequent solder activity even at ambient temperatures. The cleaning process is critical and expensive. Despite this, however, flux may remain within the cavities in the joint which results in the creation of unwanted holes an channels. These reduce mechanical strength. In addition, since fluxes are chemically agressive, these may act as a sight for corrosion and water absorption.